1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image using a two-component developer, and a control method.
2. Description of the Related Art
In recent years, most of dry-type printers and copying machines have adopted a development system using a two-component developer that is composed of toner and carrier. While toner is consumed at the time of printing, carrier remains in a developing device. Consequently, the carrier is always stirred, and the carrier may be crushed or toner may adhere to the carrier. The carrier thus deteriorates, and the development performance is degraded.
In the case of a cleanerless photoconductor body, such a problem arises that paper dust enters the developing device. The paper dust, which has once entered the developing device, will never go out. If such paper dust accumulates in the developing device, an image defect occurs and, for example, image formation may be disabled.
If means (e.g. filter) for reclaiming the developer is provided within the developing device that has a developing roller, such means may hinder conveyance of the developer.
There is known a development method that is called “occasional small-amount developer replacement method.” In this method, aside from consumed toner replenishment, new carrier (conc. toner: replenishing developer) is replenished into the developing device, and excess developer is let to overflow out of a discharge port that is formed in the wall of the developing device. Degraded developer is replaced with new toner and carrier, thereby maintaining the development performance and suppressing degradation in image quality.
In the occasional small-amount developer replacement method, however, the toner/carrier ratio is different between the developer within the developing device and the conc. toner (developer). Thus, the developer and conc. toner are not easily mixed, and non-uniformity tends to occur in the density of an output image. In addition, new developer tends to flow out of the discharge port.